The present invention relates to modifications of ophthalmic lens grinding machines for providing for differential adjustment external to the internal machine settings. More specifically, the present invention relates to a method and apparatus for adjusting the forming members of a lens bevel edger machine for providing a plurality of differentials such that various lens blank materials can be accommodated on a single bevel edger machine.
In the lens grinding industry a great number of ophthalmic labs have sprung up with the advent of modern bevel edger machines. These machines are capable of taking a lens blank and grinding a final shape of a lens for fitting of the lens in a particular frame. Thus, a lens blank of the proper prescription is rough cut to the rough shape of the frame and thereafter a bevel edge is ground on the lens such that the lens will properly fit in the glasses frame. Such procedures are known in the art and explained in the owner's manuals of AIT and WECO bevel edger machines which are incorporated herein by reference thereto.
In modern eyeglasses, lens blank materials are commonly CR 39 plastic, polycarbonate or glass. Irrespective of what type of material is used a differential is required between the rough cut edging and the final bevel edging operation such that all the chips, cracks and the like formed at the edge of the rough cut lens may be removed during the final bevel edging operation of the machine. Thus, the term "differential" in the ophthalmic industry means the difference in dimension between the rough cut edge and the final bevel edge. For instance, typically in polycarbonate or CR 39 plastic lenses the rough cut dimension is from about 0.5 to 1 millimeter larger in radial distance than in the final finished size lens. However, with materials that chip readily, such as commonly available glass, the differential must be larger, on the order of from about 11/2 millimeters to 2 millimeters to provide the necessary amount of material for removal during finish beveling.
Typically, a bevel edging machine is preset internally through a tedious series of adjustments to provide the required differential for a particular set-up, i.e. either glass or plastic. This typically requires lens grinding labs either to have two separate machines or to send out work which can not be done on the single existing machine commonly found in ophthalmic labs of today.
The purchase of a second machine would allow more flexibility to a small lens grinding lab. A second machine could be set for a different lens blank material, thus, allowing a small lab to cut its own lenses irrespective of the material of the lens. However, the cost of a bevel edger machine makes this remedy extremely cost prohibitive particularly in light of the small volume of business done in certain types of materials.
Thus, there remains a need in the art to provide a system for bevel edging of all common types of lens blank materials, including CR 39 plastic, polycarbonate and glass, in a single bevel edger machine.
Additionally, polycarbonate lenses require special dry grinding of the lens because of its thermoplastic nature. Lens grinding machines typically operate with coolant flow during grinding and thus are not set up for polycarbonate grinding. Also, polycarbonate lenses typically require special polishing of the final bevel edge external to the bevel edger machine. Therefore, it is also desirable to provide a method for bevel edging of polycarbonate lenses which require special treatment as opposed to the CR 39 plastics or other lens blank materials, while using a single machine.